The present invention relates to magnetic brush development apparatus for use with electrographic copiers/duplicators or the like and, more particularly, to improved apparatus for controlling the flow of developer material to the magnetic brush.
It is well known in the electrographic arts to use magnetic brush development apparatus for applying developer material to latent images n a photoconductor that is advanced past the magnetic brush. The developer material may initially be mixed in a sump to triboelectrically charge the material prior to delivering it to the developer roller of the magnetic brush apparatus.
It is also known to meter the flow of developer material to the magnetic brush and to gate or shut off the flow of material to the brush under certain circumstances. Metering of the developer material can be accomplished by a skive or by feeding the material through a slot leading to the magnetic brush. For example, in U.S. Pat. No. 4,538,896, toner is provided to a development station in a hopper. The hopper is closed by a plate that can be rotated to allow toner to fall through an opening in the hopper to a magnetic brush. Also, U.S. Pat. No. 3,523,518 discloses dispensing of toner from a cartridge having a series of holes therein by rotating the cartridge and allowing toner to fall through the holes in the cartridge under the influence of gravity.
It also is known to shut off the flow of developer material from a magnetic brush to a photoconductor in order to completely terminate the development of latent images on a photoconductor. For example, in color copiers having several magnetic brush development stations for applying toners of different colors to latent images it is known to move the stations relative to the photoconductor so that only one color toner at a time is applied to the photoconductor. Other ways of shutting off flow of developer material are known. See, for example, Japanese laid open patent publication No. 60-194476, published Oct. 2, 1985 and based on Japanese patent application No. 59-48060. The Japanese publication teaches the delivery of developer material from a sump to a magnetic brush for developing latent images by means of a transport roll located between the sump and the magnetic brush. The magnetic brush comprises a developer roll that is rotated in one direction to deliver developer material fromt he transport roll to the photoconductor. When it is desired to shut off the flow of developer material to the photoconductor, the developer roll is stopped and then rotated in the opposite direction so that a developer-free part of the developer roll faces the photoconductor to thereby stop application of developer to the photoconductor.
While the known prior apparatus may work satisfactorily, in some cases they may be difficult to operate as, for example, when the entire station is moved between operable and inoperable positions relative to the photoconductor. In addition, some of the prior apparatus may not provide the degree of reliability, rapid response time desired to control the flow of developer material to the magnetic brush, or complete termination of developer flow when desired.
The present invention is an improvement over commonly-assigned, copending U.S. patent application Ser. No. 944,895, filed Dec. 22, 1986 in the names of Frank Hacknauer et al and entitled "Magnetic Brush Development Apparatus Having a Gating and Metering Mechanism." The apparatus disclosed therein includes a roller for transporting developer material from a sump toward a magnetic brush, and a tube surrounding the roller and rotatable between two positions. The tube has two spaced slots that are aligned with the sump and brush when the tube is in one position so that developer material can travel from the sump to the roller through one slot and then through the other slot to the brush. When the tube is in its second position the tube slots are offset from the sump and brush to stop the flow of developer material to the brush. Thus the flow of developer material is controlled by rotating the tube a sufficient distance, e.g., 60% to offset the slots from the sump and magnetic brush. The tube may rotate a significant part of the way from its first to its second position before developer stops flowing to the magnetic brush. As a result, there may be a trailing edge of developer material that may be deposited in the interframe area between adjacent latent images on the photoconductor, and some material may even reach the latent image following the image that is to be developed, thus producing an undesirable leading edge effect on the following latent images. A more rapid shut-off of developer flow is desirable.